A Statistical and Data Management Core (hereafter referred to as the Statistical Core unit) is proposed to provide assistance in the design and development of clinical and laboratory based studies arising from this Program Project. This core will coordinate all data collection and computerized data management systems and will perform statistical analyses of data resulting from these studies. The present biostatisticians and data manager will continue in their respective roles, providing the support essential to the successful completion of this research. Besides data management, the Statistical Core will assist the PI's of each project in the design and implementation of the proposed studies. In addition, statistical modeling techniques will be explained as a means of analyzing the subclinical shedding, PCR and mucosal immunity data.